The present invention relates to a method for checking a semiconductor device in which integrated circuits of a plurality of semiconductor chips formed on a semiconductor wafer are checked in a lump in the state of the wafer.
Recently, the size of electronic equipment on which a semiconductor integrated circuit device (hereinafter referred to as a semiconductor device) is provided has been considerably reduced and the price has been remarkably lowered. With such improvements, the reduction in size and price of the semiconductor device has been required greatly.
The semiconductor device is usually supplied in the state where a semiconductor chip and a lead frame are electrically connected by a bonding wire and are then sealed by resins or ceramics, and is mounted on a printed board. However, it has been desired that a method for directly mounting, on the circuit board, the semiconductor device which is kept cut out of the semiconductor wafer (hereinafter, the semiconductor device in this state will be referred to as a bare chip) will be developed to meet the demand for reduction in size of the electronic equipment and that the bare chip having a guarantee of quality will be supplied at a low price.
In order to guarantee the quality of the bare chip, it is necessary to make a check such as burn-in on the semiconductor device in the state of a wafer. However, it takes a long time to check a plurality of bare chips formed on the semiconductor wafer one by one or every several ones many times. Thus, such a checking method is not practical in respect of time and costs. Consequently, it is required that a check such as burn-in should be made on a lot of, for example, 1000 or more bare chips in a lump in the state of the wafer.
In order to check the bare chips in a lump in the state of the wafer, it is necessary to simultaneously apply a supply voltage and a signal to the check electrodes of a lot of semiconductor chips formed on the semiconductor wafer so as to operate the semiconductor chips. Consequently, it is necessary to prepare a probe card having a large number of (usually, several thousand or more) probe terminals. A needle type probe card which causes needles to come in contact with check electrodes according to the prior art is not applicable in respect of the number of pins and the price.
A contactor formed of a thin film type probe card has been proposed, in which probe terminals comprising bumps which are connected to the check electrodes of the semiconductor chips are provided on a flexible substrate (see Nitto Giho, Vol. 28, No. 2, Oct. 1990, pp. 57-62).
A method for checking a semiconductor device using the contactor according to the prior art will be described below.
Alignment of the contactor with a semiconductor wafer is performed. Then, the contactor is pressed against the semiconductor wafer. The probe terminals of the contactor are caused to come in contact with the check electrodes of the semiconductor chips. Thereafter, a supply voltage and a signal voltage are applied to the probe terminals. Thus, the semiconductor device is checked.
Ordinarily, the check electrodes of the semiconductor chips are formed of aluminum, its alloy (Al/Si, Al/Si/Cu, etc.) or the like. Therefore, the surface of the check electrode is covered with a surface natural oxide film such as alumina or the like. In order to obtain a good electric connection between the probe terminal of the contactor and the check electrode, it is necessary to press the contactor against the semiconductor wafer to break the surface natural oxide film by the probe terminal of the contactor.
If the number of the semiconductor chips formed on the semiconductor wafer is increased, the number of the probe terminals formed on the contactor is increased so that the press force applied to each probe terminal should be reduced. For this reason, the surface oxide film cannot be broken surely by the probe terminal. Consequently, a contact resistance of the probe terminal to the check electrode is increased and a variation in contact resistance occurs. In Other words, it is hard to break the surface oxide film with a load of 10 g per probe terminal in the check electrode on which the ordinary surface oxide film is formed. Accordingly, it is necessary to apply a load of 20 to 30 g per probe terminal or to move the probe terminal in parallel with the main face of the semiconductor chip to perform scrubbing in order to break the surface oxide film surely.
In the case where the contactor is pressed against the semiconductor wafer by vacuum suction force to cause the probe terminal of the contactor to come in contact with the check electrode of the semiconductor chip, a maximum load is 1000 g per square centimeter at an atmospheric pressure. For this reason, if the number of the probe terminals is small, i.e., 50 or less per square centimeter, a load of 20 to 30 g can be kept per probe terminal. If the number of the probe terminals is large, i.e., 50 or more per square centimeter, the load is 20 g or less per probe terminal. For this reason, the surface oxide film of the check electrode cannot be surely broken by the probe terminal. In particular, if the number of the probe terminals is 1000 or more, the above problems turn out notable.
It is possible to apply, to the contactor, a load which is greater than the vacuum suction force. However, if a check is continued over a long period of time while applying a load of 20 to 30 g per probe terminal, the tip portion of the probe terminal is deformed so that the life of use of the contactor is shortened.
By moving the probe terminal in parallel with the main face of the semiconductor chip to perform scrubbing so as to break the oxide film formed on the surface of the check electrode, the probe terminal is badly worn out so that the life of use of the contactor is shortened.